1. Field of the Invention
This invention relates to a method and apparatus for engine analysis applicable to the electrodynamic analysis of electronic signals derived from an engine. An example of the application of the invention is to the analysis of the operation of a spark-ignition internal combustion engine by analysis of electrical signals derived from the spark ignition system. However, the invention is applicable to the analysis of compression ignition engines. Indeed, certain broad aspects of the invention are applicable to the analysis of signals relating to the operation of any rotary equipment, whereby the operation of the equipment can be analyzed, particularly by reference to and by comparison with expected operating parameters, such as corresponding signals relating to the engine or other equipment when operating in a substantially new condition. In this way, a measure can be obtained of the degree of divergence of the equipment from its ideal operating condition as a result of use and wear etc.
An example of an input signal which may be analyzed in accordance with the principles of the present invention is an electrical wave form derived from the spark ignition system of an internal combustion engine. Examples of other input signals and waveforms to which the present invention is applicable are electronic control unit signals, and relay switching (distributor-type ignition systems) signals. These are examples of time-based signals for analysis. In addition, as examples of signals in which analysis would be performed on a frequency basis are signals derived from vibration diagnostic equipment, such as the apparatus disclosed in our co-pending and unpublished application GB 9501380.1 (P52555GB); and oscillator outputs relating to frequency based gas sensing (such as may arise from sensing gas pressures in the crankcase or exhaust system of an automotive or other engine), or shaft encoder outputs for rotating machinery in which, for example, the encoder output frequency is dependent upon the rotational velocity of the shaft. As an example of signals where the basis of comparison is amplitude, there are power supply ripple voltages, such as might be obtained from the alternator of an automotive vehicle, and the battery charging current of such a vehicle.
2. Description of Prior Art
Conventionally, an input wave form from the spark ignition system of an internal combustion engine has been analyzed by visual techniques including the use of a suitable display on a cathode ray tube, whether in analog form for instantaneous visual analysis by a trained technician, or by digital analysis, digital recording, and subsequent simulated analog display of digitized data, in accordance with the teachings in European patent EP 08 13 53B (Bear).
The digital analysis, recording and subsequent display in simulated analog form of the above-mentioned prior patent provide the advantages of flexibility of processing of the data prior to visual display, but is inherently subject to the shortcomings of visual assessment techniques, namely the limitations of any visual assessment technique, these relating to the observer's own personal visual assessment capabilities, which vary from person to person. Moreover, such an assessment is inevitably somewhat superficial and lacks the attention to detail which would clearly be beneficial if the remedial steps to be taken following such an assessment are to be carried out with the level of precision which can be realized when modern servicing techniques are utilized to their fullest extent.
There is disclosed in U.S. Pat. No. 5,387,870 (Knapp et al.) a method and apparatus for feature extraction from internal combustion engine ignition waveforms. In this apparatus a processor means determines in real time, times corresponding to positions along an ignition wave form corresponding to firing time, beginning of dwell interval, next firing time etc, and real time values corresponding to firing peak height, firing line duration etc. These values are compared with fixed threshold values so that anomalies can be determined. No comparison is provided between the input signal and a corresponding comparison or template signal. This disclosure corresponds in its main substantive elements with the functions provided by presently available automotive test equipment in which an input waveform is compared with pre-stored data representative of the limit values (or threshold values) of the relevant waveform. However, no means is provided enabling a convenient and effective comparison of the actual input waveform with the appropriate form of that wave in its ideal condition or format.
U.S. Pat. No. 5,119,315 discloses a method of correlating an input mass chromatogram with reference chromatogram data.
The prior art appears to contain no disclosure of a process whereby convenient comparison between an input signal from an actual operating machine can be analyzed by reference to the corresponding waveform as produced by its ideal counterpart, for example the machine in new form.